Fluid systems are used in a wide variety of applications, particularly in the automotive field. For example, fluid systems are used to transfer power (e.g., automotive brakes), boost power (e.g., automotive power steering), and provide cooling (e.g., automotive radiator system or air conditioner). Fluid systems use a working fluid to transfer forces used in such applications. When in the confines of a closed loop fluid system, the working fluid is under pressure and is in a liquid form.
When filling a fluid system with a working fluid for the first time, it is important to remove as much air from the system as possible. Traditionally, initial working fluid introduction is performed by first evacuating air from the system through a port using a vacuum or similar device. The working fluid is then introduced into the system under low pressure (e.g., under its own weight). With a standard automotive power steering system, the evacuation and fill procedure can take up to about two minutes or more.
During the filling process, air can sometimes become trapped within the system. In most closed loop fluid systems, the presence of air in the system is undesirable. For example, in power steering systems air can cause the pump motor to burn out prematurely, and in brake systems air can cause decreased responsiveness of the brakes. In an attempt to remove trapped air from the system, a newly-filled system is typically "burped" by running the system through a number of cycles to force air trapped in the system to be brought to the surface of the fluid reservoir. The system is then topped off with an additional amount of working fluid to replace the air that has been removed. It is not uncommon for it to take 4 to 6 hours to adequately burp a closed loop fluid system.